The sinking of the Costa Concordia, the luxury liner that struck rocks off Italy's west coast Saturday, has raised questions about the safety of cruise ships.

The ship was carrying 4,234 passengers and crew on its weekly route when investigators say it got dangerously close to the shore. The rocks tore a 160-foot long gash in the hull, causing the ship to tip and sending passengers scrambling to the deck.

Like a scene from the movie "Titanic," vacationers reported forcing their way onto lifeboats and jumping into the icy waters to swim to safety -- a far cry from the carefree cruises advertised on TV. But experts say cruise ships have a good track record, and that failsafes and emergency plans should keep everyone aboard safe, even in the event of a mishap.

"Cruise ships have a redundancy of back-up systems," Aaron Vanhuysen of the U.S. Coast Guard told ABC News. "If they lose one of their generators, they have a back-up emergency generator. If they lose a fire pump, they have another fire pump they can access as well."

Cruise ships are designed with their hulls divided into watertight sections. Even if two sections are breached, the ship will stay afloat. They also have sophisticated navigation systems: sonar; radar; and GPS to guide the crew.
And in the event of an emergency -- whether it's a rogue wave, a sudden steering problem or a fire on board -- cruise ships are required to have enough life jackets and lifeboat space for everyone. They're also required to hold an evacuation drill within 24 hours of setting sail. For those on the Costa Concordia, the drill was scheduled for the following day.

The Costa Concordia was carrying 4,234 passengers and crew when it hit the rocks near Giglio, a small island off the coast of Tuscany. Investigators say the ship was an "incredibly close" 150 meters (roughly 500 feet) from the shore.

Scuba divers reportedly found two more bodies in the submerged part of the ship today, bringing the death toll to five. Before the bodies were found, 17 people remained unaccounted for -- 11 passengers and six crew members.

Experts are still analyzing the ship's black box, which has already revealed a one-hour lag between the time of the impact on the rocks at 9:45 p.m. local time and the ship's alarm call to the coast guard at about 10:43 p.m.

Schettino was in custody today, facing possible charges of manslaughter and abandoning his ship. Schettino reportedly left the stricken vessel at approximately 12:30 a.m., while many passengers didn't get safely off the ship until 6 a.m., Ansa reported.

The Costa Concordia crash is one of the worst cruise line disasters in recent years. In 2005, a 70-foot wave tore through the Norwegian Dawn -- an ocean liner en route from the Bahamas to New York City. Four passengers were treated for minor injuries. And in 2010, three large waves struck the Louis Majesty off the coast of Spain, shattering windows and flooding several floors of the ship. Two passengers were killed.

An estimated 15 million people hopped aboard cruise ships in 2010, the majority of them Americans.